The present invention relates to a fuel supplying device for an internal combustion engine, and more particularly to a fuel supplying device for an internal combustion engine employing a so-called "single point injection" in which a single or a plurality of fuel injection valves or nozzles inject fuel into the inside of a collector section of an intake manifold from which a plurality of branches extend toward cylinders of the engine.
The construction of a conventional "single point injection" type fuel supplying will be described hereinafter in connection with FIG. 1. It comprises an intake manifold 1 including a plurality of branches 2 extending outwardly from a collector or riser section 3 having a bottom wall 4, which serves as a heat exchanger disposed adjacent to or projecting into a riser of the exhaust manifold to be heated thereby. A substantially straight induction passage 5, more particularly, a throttle chamber having mounted therein a throttle valve 6, is connected to the riser section 3 coaxially. A fuel injection valve or nozzle 7 is mounted to the riser section 3 to communicate with the inside thereof at the upper portion of peripheral wall of the riser section 3 so that jet of fuel injected from the fuel injection valve 7 is directed radially inwardly to cross a stream of air flowing into the riser section 3 from the induction passage 5. As the jet of fuel crosses the stream air, the fuel will be atomized to facilitate mixing of the fuel with the air and thus to achieve even distribution of the fuel between the branches 2 leading to the cylinders. The quantity of fuel to be injected per each injection is varied under the control of a control unit (not shown) in response to the output from an air flow sensor (not shown). If a pulse responsive type injection valve is used, it must be actuated to inject fuel twice per each revolution of the engine crankshaft in the case of a 4-cylinder internal combustion engine, while, it must be actuated to inject three times per each revolution of the engine crankshaft in the case of a 6-cylinder intenal combustion engine. With the conventional fuel supplying device in which fuel is injected toward the opposite wall of the riser section 3 to cross a stream of air flowing therethrough, the difficulty encountered is that, during a certain mode of engine operation, a considerable portion of the injected fuel will flow downwardly along the wall of the riser section 3, so that the quantity of fuel actually reaching each of the engine cylinders will be far below that quantity of fuel required by the control unit in response to the output of the air flow sensor. The poor response characteristics of this fuel supplying device becomes particularly significant if used in a so-called "feed back" or "closed loop" control system. The "feed back" control system uses an exhaust sensor provided in the engine exhaust system and a control unit which varies the quantity of fuel to be fed to the engine cylinders in response to the output from the exhaust sensor so as to maintain the air fuel ratio at a preselected level. Therefore, this control system is known as one of effective measures for operating an internal combustion engine provided with a three-way catalytic converter which can perform HC and CO oxidation NOx reduction. However, the response characteristics of the conventional fuel supplying device as described above is so poor that the precise control of the engine with the "feed back" control system is hardly possible.
It will now be apparent from FIG. 2 that response time or characteristics of the single point injection with the fuel injection valve arrangement of the conventional fuel supplying device is slow. This comes from the comparison of a response characteristics curve c of the conventional fuel supplying device shown in FIG. 1 with that a of another fuel supplying device using a carburetor (carburetor induction) and that b of the other fuel supplying device in which fuel is supplied to the engine cylinders from individual fuel injection valves, respectively (EGI).